Triangular structures are used widely in the building industry, mainly for buildings with single-or double-curvature surfaces, such as cylindrical, rotational or spherical surfaces, cylindrical roofs, rotational cooling towers or dome structures. An example of a building having cylindrical and rotational surfaces is the Oakland Coliseum of Oakland, Calif.
Composite structural systems are also known and have been used in the building industry. In such systems, compression chords of trusses advantageously use lighter steel forms and create compression elements by filling the forms with concrete. Composite columns with heavy steel outside forms have also been used to minimize structural steel, heavy lifting, cost of fireproofing and construction time.
Exoskeleton structures have also been known and used in the past. They have been built for cooling towers, water towers and other tower structures. Several of the existing high-rise office buildings in the U.S. also use exoskeleton or outside supporting structures.
Composite space trusses were built and used in Hungary in the period of 1960 to 1970, using the advantages of the composite action of the two materials of light steel and concrete. Horizontal chord members of such trusses were filled with concrete. The prefabricated pyramid elements were produced in large series and were light enough to lift them into final position using heavy equipment. The structural solution and details of these trusses, however, do not solve existing building problems inasmuch as they are not applicable for all supporting exoskeleton structures.
Composite vertical columns using light weight pipes on the external facades of high-rise office buildings have been proposed. Such columns suggested the use of vertical pipes fabricated in two halves. Also, reports have been published on steel-formed pipe columns which have been strengthened by high-strength concrete fill. This use of composite columns results in a rigid architecture. Close rows of heavy circular columns dominate the facades. However, these composite columns do not use the higher lateral rigidity of triangular exoskeleton structure and produce natural architectural forms.
Exoskeleton structures with triangular structural networks are also known in the industry. Domed buildings with exoskeleton structures have been built using triangular half elements with serial fabrication. The bottom row of the triangular elements of such structures start from ground level.
Other exoskeleton structures for towers have also been known; for example, such a structure can be found in the circular tower built for the Port of Kobe, Japan. Other towers, such as hyperbolic cooling towers, use exoskeleton structures. However, neither the domes using triangular exoskeleton structure nor the known tower structures use light steel formings filled with concrete. Such structures use either pure metals or are made with reinforced concrete structures.
Exoskeleton structures have also been proposed for use on buildings with heavy steel structure in box shape or in pipes fabricated from steel plates with thickness up to 80 mm. These suggested structures need heavy lifting equipment and costly and time-consuming site welding procedures done at elevated locations up to 1000 feet above the ground. Most of these structures are expected to be fabricated in faraway places, even in overseas plants; thus, the cost of shipping also increases the cost of erection of the structures.